1. Field of the Invention
This invention relates to the field of liquified gases such as carbon dioxide and nitrogen and particularly to an apparatus and method for balancing the discharge of such liquified gases through a multi-orifice manifold.
2. Description of the Prior Art
Liquified gases such as liquified nitrogen and liquified carbon dioxide are used extensively for the rapid chilling of various products, especially food products. Normally, food or other products to be chilled are moved by means of a conveyor belt through a freezing tunnel or enclosure containing an overhead arrangement of spray nozzles. The liquified gas is sprayed onto the products to be frozen as they pass through the freezing tunnel.
Liquified gases are stored under high pressures in order to maintain their liquified condition. Upon introduction into a manifold containing multiple discharge orifices, a considerable pressure reduction takes place. This results in a mixture of vapor and liquid. When the rate of flow within the manifold is not turbulent, the liquid and vapor separate with the liquid on the bottom and the vapor on the top. In this instance, the discharge orifice which is closest to the source of supply discharges liquid, and the discharge orifice farthest away from the supply discharges vapor. The intervening discharge orifices contain a mixture of liquid and vapor.
This condition is highly unsatisfactory, since it is desired to have equal amounts of liquid discharged from each of the discharge orifices of the manifold in order to provide rapid and balanced chilling of the product.
The above condition could be alleviated at least in part by sizing the discharge pipe for turbulent flow, or including pipe mixers or individual orifice mixers. However, these methods are not applicable to different orifice sizes, different orifice configurations, or differences in specific pressures. In addition, the extremely cold temperatures of the liquified gases can produce special problems. For example, such devices and methods could be unworkable due to the possibility of the production of ice in the case of liquid carbon dioxide which could freeze solid and plug the lines entirely.
As a consequence of the above problems, it is desirable to be able to control or balance the mass flow rate per orifice during the reduction of pressure. Ideally, such a solution should be relatively simple to avoid any problems with snow or ice buildup.